docs: def txtopn(fname):
      """
      Internal undocumented command for opening a new text file for
      subsequent write access.
  
      https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/ftncls_c.html#Files
      https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/ftncls_c.html#Examples
  
      :param fname: name of the new text file to be opened.
      :type fname: str
      :return: FORTRAN logical unit of opened file
      :rtype: int
      """
      fnameP    = stypes.stringToCharP(fname)
      unit_out  = ctypes.c_int()
      fname_len = ctypes.c_int(len(fname))
      libspice.txtopn_(fnameP, ctypes.byref(unit_out), fname_len)
      return unit_out.value